1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting data in a wireless communication system.
2. Related Art
In wireless communication systems, it is necessary to estimate an uplink channel or a downlink channel for the purpose of the transmission and reception of data, the acquisition of system synchronization, and the feedback of channel information. In wireless communication system environments, fading is generated because of multi-path time latency. A process of restoring a transmit signal by compensating for the distortion of the signal resulting from a sudden change in the environment due to such fading is referred to as channel estimation. It is also necessary to measure the state of a channel for a cell to which a user equipment belongs or other cells. To estimate a channel or measure the state of a channel, a reference signal (RS) which is known to both a transmitter and a receiver can be used.
A UL reference signal may be divided into a demodulation reference signal (DMRS) and a sounding reference signal (SRS). The DMRS is a reference signal used in channel estimation for the demodulation of a received signal. The DMRS may be associated with the transmission of a physical uplink shared channel (PUSCH) or physical uplink control channel (PUCCH). The SRS is a reference signal transmitted from a user equipment (UE) to a base station (BS) for UL scheduling. The BS estimates an UL channel through the received SRS and uses the estimated UL channel in UL scheduling.
Meanwhile, the SRS may be periodically transmitted. Alternatively, when the base station needs transmission of the SRS, the SRS may be aperiodically transmitted by being triggered by the base station. A subframe in which the SRS is configured to be transmitted may be pre-determined. The subframe in which the SRS is configured to be transmitted may be a subframe to which a PUSCH and a PUCCH are simultaneously allocated.
When the PUSCH corresponding to a random access response grant is allocated to a subframe in which an aperiodic SRS is configured to be transmitted, a definite operation of the UE is required.